In a microwave safe bowl, melt butter and chocolate for about 1 minute.

Remove and stir well.

You really want to use the heat within the butter and chocolate to melt the rest of the clumps.

If you microwave until it's all melted, you've overcooked the chocolate.

So get a spoon and start stirring.

Add 10 seconds if needed but stir well before you decide to do that.In a bowl, add eggs, sweetener, and vanilla and blend until light and frothy.Pour the melted butter and chocolate into the bowl in a slow stream and beat again until it is well-incorporated.

Pour the mixture into greased springform container or cake pan and bake at 350F for 30-35 minutes until a knife inserted in the center emerges clean.Serve with whipped cream if desired (see note)